I am designing a custom PCB with ESP32 PICO MCU. I am going to use BLE peripheral mostly in my application. I have some questions regarding

  1. Which type of Antenna should I choose for my application?

  2. The flash memory of ESP32 PICO is 4MB according to the datasheet. My code size is not anyways going to exceed that memory size. So, can I skip integrating the external flash module or is it compulsory to have it?

Basically my application involves collecting data over I2C from an MPU6050 gyro sensor and transmitting those values through BLE. I must be able to read data using my terminal app in the phone. I am planning to use this ceramic antenna.

I have another doubt regarding the impedance matching circuit. The input impedance of the antenna is 50 Ω and the ESP32 PICO's impedance is also 50 Ω according to the datasheet. Can I remove the impedance matching circuit on my board or should I have it as the theoretical values might swing around a little bit?

  • \$\begingroup\$ What is your power source? If running on battery, what’s your intended battery life? How often do you need to transmit or do any work? What are your expected sleep patterns? The ESP32 is a great chip, but ESP32, BLE and deep sleep are not good friends, so in such a scenario you would probably be better off with a different chip. If you don’t care about sleep then you can definitely go ahead with it. \$\endgroup\$
    – jcaron
    Commented Dec 18, 2019 at 13:13
  • \$\begingroup\$ Yes I don't much deal with deep sleep modes. The frequency of data transmission would be for every 200 milli seconds. I am planning to run my ESP boards with a 3.7V Li-ion battery as of now....but also have a plan of using coin cell. \$\endgroup\$
    – kowshik
    Commented Dec 18, 2019 at 16:31
  • \$\begingroup\$ How long do you want the device to run on that battery? Without deep sleep, it’ll only last a few days at most on even a pretty large LiPo, and hours on a coin cell... \$\endgroup\$
    – jcaron
    Commented Dec 18, 2019 at 21:47

1 Answer 1

  1. What does your application do? Do you want to design the copper traces yourself for the antenna or a working module is good enough? Start by googling BLE antennas or go to your distributors website. You can use an external antenna or make a design for single ended RF output. See https://www.esp32.com/viewtopic.php?t=1635 for more info. Seems like a default layout is fine.

  2. Yes, you don't need extra flash memory on the board when you're not going to use it

Ok, you already have your antenna. And no, you don't need an impedance matching circuit as they are already matched. The difference between theoretical and practical will be negligible. Remember that the passive components in the matching circuit also won't be perfectly matched with the theoretical values.

  • \$\begingroup\$ I have added my comments to my question. Please let me know your idea...thanks in advance..!! \$\endgroup\$
    – kowshik
    Commented Dec 18, 2019 at 12:05
  • \$\begingroup\$ @kowshik updated my answer \$\endgroup\$
    – Swedgin
    Commented Dec 18, 2019 at 14:28
  • \$\begingroup\$ I would like to clarify one more....How to deal with bypass capacitors? I am noticing many caps near the VDD, Sensor_Vp kinda pins in the reference design which I am not using any way. So, how can I know which parts are redundant so that I can keep my design compact..!! \$\endgroup\$
    – kowshik
    Commented Dec 18, 2019 at 16:34
  • \$\begingroup\$ @kowshik I wouldn't omit the bypass caps on VDD and place them as near to VDD as possible. If you're sure you won't use Sensor_Vp than I suppose you can omit them. How to know which parts are redundant? No parts, except the ones connected to pins you won't use. !You are using VDD! \$\endgroup\$
    – Swedgin
    Commented Dec 18, 2019 at 17:27
  • \$\begingroup\$ I have a doubt regarding programming my board. I am not going to have USB to TTL IC like CP2102 on my design. I would like to know whether I can use Arduino or any external programmers to upload code to my ESP32 using UART? \$\endgroup\$
    – kowshik
    Commented Dec 19, 2019 at 19:02

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